In wireless communication, radio frequency (“RF”) spectrum is a resource that typically gets rationed out to telecommunication providers by government agencies in each of the various jurisdictions. In 2008, for example, the United States Federal Communications Commission (“FCC”) auctioned off blocks (“bands”) of the spectrum to cellular service providers to be used for Long-Term Evolution (“LTE”) communication. However, the FCC reserved parts of the spectrum for use by public safety agencies, Band 14 (FDD: 788-798 MHz uplink, 758-768 MHz downlink) being a well-known example. Other jurisdictions have similar set-asides for public safety.
In spite of operating on different frequencies, a User Equipment (“UE”) on a commercial network often runs the risk of interfering with UEs on public safety networks. This is particularly true when the two types of networks operate on adjacent bands. For example, cellular customers on some networks use Band 13 for cellular communication. Band 13 is adjacent to a public safety band. Therefore a customer on a Band 13 networks may unknowingly interfere with public safety UE.
To prevent operators from interfering with one another, government agencies often mandate the use of guard bands, in which an operator is required to leave a buffer zone between its allocated band and the adjacent band. But because RF spectrum is a limited resource, government agencies have relaxed these guard band requirements. In the United States, for example, guard bands of 2 MHz or less are now the norm.
Having smaller guard bands has posed challenges to wireless network operators, especially when the receive frequencies of one service are spectrally near the transmit frequencies of another service. This is because wireless users are geographically unrestricted, so there will likely be many situations in which the wireless transmitter of the first operator and spectrally adjacent wireless receiver of the second operator are close to one another, e.g., one meter or less.
With such low path loss and frequency separation between the transmitting device and the receiving device, the wireless transmitter needs to be able to reduce its transmit power to avoid interfering with the nearby wireless receiver.